This application claims foreign priority benefits under 35 U.S.C. xc2xa7119 from Australian Patent Application Serial No. PQ5910 filed Feb. 29, 2000.
The present invention relates to a cartridge shell and a corresponding cartridge for blast holes for the purpose of fracturing hard materials. The invention further relates to a method of use of such a cartridge and in particular a method of charging blast holes with the cartridge.
A typical cartridge shell for a blast hole is in the form of a cylindrical tube closed at both ends. Some cartridges may contain only an energetic substance while others may contain both an energetic substance and an initiator. The cartridge will be inserted to reside near the toe of a blast hole drilled or otherwise formed in a rock or other hard material to be fractured. The hole may then be stemmed with a particulate stemming material. When the energetic material in the cartridge is initiated there is a rapid generation of gas and thus a rapid build up of gas pressure near the toe of the hole. Provided that the gas generated is contained for a short period of time the resulting gas pressure may cause fractures to be propagated from the hole through the hard material.
The efficiency and effectiveness of this process is largely determined by factors such as the provision and quality of a gas seal formed on the side of the cartridge nearest the collar of the blast hole and the ability to hold the seal in position. Clearly if the seal is poor, gas will escape around the seal thereby reducing gas pressure as well as the rate of gas pressure increase. Further, the escaping gas has adverse effects in terms of ejecting stemming from the blast hole, generation of recoil and producing flyrock. However, even if the seal is one of high integrity, if the seal is not held firmly in place and is able to be pushed back toward the collar of the hole then the physical volume of the confined space within the hole in which the gas acts increases, thereby decreasing the gas pressure.
It is an object of the present invention to provide a cartridge shell and associated cartridge that in use may assist in alleviating the above noted deficiencies. It is a further object of the present invention to provide a method of charging a blast hole with such a cartridge.
According to a first aspect of the present invention there is provided a cartridge shell for use in fracturing hard materials, said shell including at least: a main body defining a volume for holding an energetic material, the body having a first and second opposite ends, the first end being generally planar and the second end being tapered to form a point or wedge-like member directed away from the first end.
Preferably the main body includes a line or zone of weakness adjacent to the first end.
Preferably the cartridge shell includes a closure device at the first end said closure device being provided with, or in conjunction with the main body defining, the line or zone of weakness.
Preferably the main body is provided with an opening at the first end and the closure device comprises a cap for closing said opening.
In one embodiment, the cartridge shell further includes an aperture at the first end through which an initiator lead passes. Preferably the aperture is formed in the closure device.
Advantageously, the cartridge shell includes a recess passageway on an outer surface about the first end to seat the initiator lead.
In an alternate embodiment the cartridge shell includes an aperture in or near the second end through which an initiator lead passes. In this embodiment the cartridge shell may include an internal recess or passageway through which the initiator lead extends.
Preferably the second end is provided with two or more inclined surfaces that converge toward each other in the direction from the first end to the second end.
However, in an alternate embodiment, the second end is in the form of a conical frustum.
According to a second aspect of the present invention there is provide a shell for a cartridge for use in breaking and/or fracturing of hard material by the insertion of the cartridge followed by particulate stemming material in a hole and subsequent initiation of the cartridge, the shell including at least a main body defining a volume for holding an energetic material, the body having first and second opposite ends, the second end including a surface for exerting a radial compressive force on the stemming material in use.
According to a further aspect of the invention there is provided a cartridge for use in fracturing a hard material, the cartridge comprising at least:
a cartridge shell in accordance with the first or second aspect of the present invention and a quantity of an energetic material held within the main body of the cartridge shell.
Preferably the cartridge further comprises an initiator disposed within the main body.
Preferably the cartridge further includes an initiator lead connected at one end to the initiator and passing through an aperture in the cartridge shell.
Preferably the energetic material is a propellant.
Preferably the initiator is a non-explosive initiator.
Preferably said cartridge includes a booster for the initiator.
In an alternate embodiment, said cartridge further includes one or more booster cartridges each containing a quantity of energetic material, said one or more booster cartridges connectable in an end to end fashion with said first end of said main body and with each other whereby the total quantity of energetic material contained by the cartridge is varied by connecting one or more booster cartridges to said main body.
Preferably said main body and each of said booster cartridges each contain no more than 10 gm of energetic material.
Preferably each booster cartridge has a first engaging means at a first end and a second complimentary engaging means at a second opposite end whereby the first engaging means of a booster cartridge is engageable with a second engaging means of an adjacent booster cartridge.
Preferably said first engaging means is received inside said second engaging means so that an outer surface of a plurality of connected booster cartridges is of substantially constant outer diameter.
Preferably each booster cartridge includes a substantially cylindrical body of a first outer diameter; an axial extension at said first end forming said first engaging means of a second reduced outer diameter; and, a recess at said second end forming said second engaging means, of an inner diameter less than the outer diameter of the axial extension to enable said first engaging means to fit inside said second engaging means.
Preferably said first engaging means and said second engaging means are relatively configured relative to each other to provide an interference fit therebetween.
Preferably said axial extension includes a plurality of circumferential, axially spaced apart ribs.
In an alternate embodiment said first and second engaging means are threadingly engageable with each other.
Preferably said booster cartridges are closed at opposite ends by respective webs, where said webs are combustible, or frangible, or both combustible and frangible.
According to a further aspect of the present invention there is provided a cartridge shell including at least;
a primary shell having a main body defining a volume for holding an energetic material, the main body having first and second opposite ends, the second end being tapered to reduce in transverse area away from said first end; and,
one or more secondary shells, each secondary shell having a generally cylindrical body for holding a volume of energetic material, said one or more secondary shells releasably connected in an end to end manner with said first end of said primary shell and with each other.
According to a further aspect of the invention there is provided a method of charging and stemming a blast hole in a hard material, the blast hole having a collar adjacent a free face of the hard material and a toe at the opposite end of the hole, the method including at least the steps of:
inserting a cartridge in accordance with the second aspect of the present invention into the blast hole with the second end of the cartridge facing the collar of the blast hole;
providing a particulate stemming material comprising a mixture of a dry binding agent, fines and coarse material;
depositing said stemming material into said hole;
mechanically holding the stemming in the hole.
Preferably said depositing step includes blowing said stemming material into said hole.
Preferably said method further includes the steps of blowing the stemming material into the hole to a level below the free surface of the hard material; inserting a stemming bar into the blast hole to bear at one end on the stemming material with an opposite end of the stemming bar extending from the free face of the hard material; and, mechanical holding said opposite end of the stemming bar.
Preferably said method includes the step of forming one end of the stemming bar with a point or wedge-like member directed away from the opposite end of the stemming bar.
Preferably said method further comprises the step of injecting a volume of a liquid or gel into the blast hole after insertion of the cartridge to fill any space between an outer surface of the cartridge and the hole and provide a liquid or gel layer between the second end of the cartridge and the particulate stemming material.
Preferably when the method is used in an underground mine having a wall in which the blast hole is formed and an opposite wall, the step of mechanically holding the stemming in the hole includes the step of operating a jack so that one end of the jack bears on the wall over the blast hole while an opposite end of the jack bears on the opposite wall.
According to a further aspect of the invention there is provided a stemming material for use in charging a blast hole the stemming material comprising a mixture of a dry binding agent, fines, and coarse material.
Preferably the binding agent is one of the group consisting of fly ash; smelter waste material; or other fines containing cementitious material.